Pneumonia in an elderly Tibetan male caused by Shewanella algae: A case report

Rationale: Shewanella algae are Gram-negative bacteria that are widely found in aquatic habitats and rarely cause lung infections in inland areas. Patient concerns: Cough with light-yellow phlegm for 2 weeks. Diagnoses: The final diagnosis was bacterial pneumonia. Interventions: The patient was treated with ceftazidime (2 g, every 12 h) for 1 week. Outcomes: The patient’s lung infection improved and he was discharged. Lessons: This case highlights a rare occurrence of lung infection caused by Shewanella algae in elderly Tibetan men residing in non-marine environments.


Introduction
Shewanella algae are widely distributed, non-fermenting, Gram-negative bacteria found in aquatic habitats. [1]This infection is typically observed in individuals with compromised immune function following trauma from open water. [2]t is known to cause various types of infections, including skin and soft tissue infections, otitis media, vertebral discitis, bloodstream infections, and abdominal infections. [3,4]However, recent global reports have indicated that Shewanella infections are not limited to tropical and temperate regions during summer, nor are they exclusive to individuals in contact with open water.Cases of Shewanella infections occurring in non-tropical regions and individuals not exposed to open water have been documented. [5,6]This case report describes the rare occurrence of pneumonia caused by Shewanella algae in an individual who consumed raw shrimp in inland China.Shewanella are uncommon opportunistic pathogens that cause pneumonia.This case highlights the significance of Shewanella as an uncommon opportunistic pathogen capable of causing pneumonia and serves as a crucial reminder for physicians to be vigilant about the potential of Shewanella algae to cause infections at various anatomical sites.

Chief complaints
A 68-year-old Tibetan male presented to our neurology clinic complaining of persistent cough with light-yellow phlegm for 2 weeks.

History of present illness
Symptoms started 2 weeks before the persistent cough with light-yellow phlegm, without any apparent cause.He measured his body temperature at home and recorded it as 37.3 °C, along with experiencing chills.He took unspecified medications independently, but the symptoms did not improve significantly.In addition, the patient reported fatigue and shortness of breath after physical activities.He denied experiencing chest tightness, palpitations, nausea, or vomiting.Owing to these symptoms and a history of related neurological disorders, the patient sought further treatment in the neurology department.Sequential Organ Failure Assessment score: 3; confusion, urea, respiratory rate, blood pressure, age >65 score: 2.

Personal and family history
Nothing in particular.

Physical examination
On examination, the patient had: body temperature, 36.5 °C; pulse rate, 80 beats/min; respiratory rate, 20 breaths/min; blood pressure, 138/84 mm Hg; oxygen saturation level, 98% (in an unoxygenated state).General examination revealed normal development, good nutrition, consciousness, autonomous posture, acute illness, physical examination cooperation, entering the ward, and normal gait.Respiratory sounds in both lungs were rough; respiratory sounds in the right lung were low, audible, and wheezing, heart rhythm was absolutely irregular, first heart sound varied in strength, pulse rate was less than heart rate, heart sound varied in strength.No split heart, heart murmur, pericardial friction, and additional heart sound was heard.Direct percussion caused pain near the posterior superior iliac spine on both sides.

Laboratory examinations
Blood test results revealed the following: white blood cell count, 10,030/μL and procalcitonin 0.067 ng/mL.A screening test for the respiratory 2019-novel coronavirus using throat swabs yielded negative results.Liver function tests revealed levels of albumin, 37.5 g/L (normal range, 40-55 g/L) and adenosine deaminase, 23.9 U/L (normal range, 4-18 U/L), whereas renal function tests revealed levels of urea, 18.3 mmol/L (normal range, 3.6-9.5 mmol/L) and creatinine, 264.0 μmol/L (normal range, 57-111 μmol/L) and glomerular filtration rate, 21 mL/min (normal range, 80-120 mL/min); no other abnormalities were found.The lower respiratory tract [epithelial cells < 10/lower power field and leukocytes > 25/ lower power field] was collected and cultured, and a Gram-negative bacterium that tested positive for oxidase was isolated after 24 hours of incubation.The bacterium was further identified as Shewanella algae using a BioMerieux VITEK 2 Compact, matrix-assisted laser desorption/ionization time of flight mass spectrometry (Autof ms1000), and 16S ribosomal RNA gene sequence analysis (Fig. 1).The drug sensitivity was detected by broth microdilution method recommended by Clinical and Laboratory Standards Institute, and the drug sensitivity was judged according to Clinical and Laboratory Standards Institute relevant standards.Antibiotic susceptibility results are presented in Table 1.

Final diagnosis
The final diagnosis was bacterial pneumonia, and other diagnoses included grade 2 hypertension (very high risk), type 2 diabetes, secondary epilepsy, coronary atherosclerotic heart disease, atrial fibrillation, chronic kidney disease stage 4, renal anemia, and lacunar infarction.

Treatment
The patient was treated with ceftazidime (2 g, every 12 h) for 1 week, which improved the pneumonia symptoms.The patient was then discharged.

Outcome and follow-up
In June, the patient reported being in a good condition.In July, the patient returned to Lhasa, which is at an altitude of approximately 3000 m, and did not experience any respiratory symptoms.

Discussion
Shewanella algae is primarily known as an opportunistic pathogen that commonly causes skin and soft tissue infections, followed by bloodstream and biliary tract infections. [5,6]Other types of infections are rarely reported, and most cases occur in coastal areas or in individuals exposed to seawater and seafood. [7]10] After obtaining the identification results, the patient's medical history was reviewed, and it was discovered that the patient had a history of raw shrimp consumption prior to disease onset.This led to speculation that this was the most likely route of infection in this case, which aligns with the findings of some studies. [11]y points • Shewanella algae are opportunistic pathogens with definite life histories that usually cause diseases.Shewanella algae can not only cause skin and soft tissue infections and otitis media, but also cause lung infections, especially in people with underlying diseases.Although the symptoms of lung infection did not cause serious adverse consequences, it reminds us that their scope of influence is expanding and needs to be considered.However, in most cases where patients have a history of consuming raw shrimp, biliary tract infections are the most common, with occasional cases of gastroenteritis being reported. [12]espiratory infections caused by Shewanella are rare.
One study analyzed 273 strains of Shewanella spp.(96 strains of Shewanella algae) published in PubMed between January 1978 and June 2022. [6]It included 19 strains of Shewanella spp. in China, which caused chest infections in 12 (4.4%)cases.Another report showed that the proportion of respiratory infections caused by Shewanella spp. was 13%. [13]Another study found that only 6 out of 29 isolated Shewanella spp.infection strains were Shewanella algae. [14]Therefore, it can be inferred that pneumonia caused by Shewanella algae is rare.
A study in Hong Kong [8] showed that 1 of every 6 cases of marine exposure was pneumonia.Other pathogens were detected at the same time, and it was determined that the possible pathogen was Shewanella spp.However, whether the pneumonia was caused by Shewanella algae was unclear.Therefore, reports of pneumonia caused by Shewanella algae are rare, particularly in China.
This case report describes pneumonia in an elderly Tibetan male with underlying diseases in inland China.Although the patient had multiple complex underlying diseases, the prognosis of pneumonia was good.Shewanella algae are often sensitive to third-generation cephalosporins, aminoglycosides, and quinolone antibiotics, but resistant to colistin and sulfonamides. [1]n this case, the patient was empirically treated with the thirdgeneration cephalosporin ceftazidime before the pathogen was clearly identified, and the patient's condition improved after 1 week of use.
Notably, climate change may be associated with an increase in the number of Shewanella.The temperature of marine ecosystems can promote the growth and expand the reach of these pathogenic microbes in subtropical humid climates.Additionally, economic development has led to the expansion of fresh marine biological transport, which may contribute to the expansion of marine pathogenic microorganisms.

Conclusion
This report describes a unique case of pneumonia caused by Shewanella algae in inland China, with a history of raw shrimp consumption and underlying diseases.Shewanella algae are causing an increasing incidence of human infections in inland areas; however, pneumonia is rare.This case suggests that Shewanella algae cause more infections and increase the possibility of more site of infections with the expansion of marine biotransport.In terms of clinical diagnosis and treatment, this case can improve the understanding, diagnosis, and treatment abilities of physicians dealing with Shewanella algae infections in inland populations.

Figure 1 .
Figure 1.Pure culture of blood agar culture-medium.

Figure 2 .
Figure 2. Chest computed tomography results of the patient after admission.

Table 1
Results of antibiotic susceptibility testing against isolates in the study.